Preparation of alkanolamines

ABSTRACT

Alkanolamine compositions are disclosed. The composition comprises an alkanolamine and hydroxylamine or hydrazine. Preferred alkanolamine includes diethanolamine, triethanolamine, and mixtures thereof. The composition of the invention has significantly reduced discoloration.

FIELD OF THE INVENTION

The invention relates to alkanolamines. More particularly, the inventionrelates to alkanolamines that have improved color stability.

BACKGROUND OF THE INVENTION

Alkanolamines, for example, triethanolamine, are widely used in cosmeticand pharmaceutical products such as soaps, cleaners, and shampoos. Oneproblem associated with the use of alkanolamines is discoloration. Thatis, during storage, the color of alkanolamines deepens, making themunsatisfactory for certain applications.

Methods for improving color stability of alkanolamines are known. Forinstance, U.S. Pat. No. 6,323,371 discloses the preparation ofalkanolamines having improved color quality by treating thealkanolamines with phosphorous acid or hypophosphorous acid prior todistillation. The pretreatment, although producing alkanolamines havinglow fresh color, does not effectively prevent the discoloration duringthe product storage.

U.S. Pat. No. 3,207,790 describes a process for improving the colorquality of alkanolamines by the addition of alkali metal borohydride tothe alkanolamines. However, the addition of alkali metal borohydridedoes not produce satisfactory results.

New improvement for the color stability of alkanolamines is needed.Ideally, the alkanolamines would remain on-the-spec color (APHA colorless than 50) for at least 3 months at room temperature.

SUMMARY OF THE INVENTION

The invention is an alkanolamine composition. The composition comprisesan alkanolamine and a color stabilizer selected from the groupconsisting of hydroxylamine, hydrazine, and mixtures thereof.Hydroxylamine or hydrazine is present in the composition in an amounteffective to reduce the discoloration of the alkanolamine. Thecomposition of the invention remains on-the-spec color (APHA color 50 orless) for at least three months in storage.

DETAILED DESCRIPTION OF THE INVENTION

The composition of the invention comprises an alkanolamine and a colorstabilizer selected from the group consisting of hydroxylamine andhydrazine.

The composition of the invention remains on-the-spec color (APHA color50 or less) for at least three months in storage at a room temperature(below 38° C.). The color is tested according to an empiricallydeveloped method. The test is performed at 60° C. Three days of thecolor stability at 60° C. is equivalent to that of one month at 38° C.Preferably, the composition remains an APHA color less than 50 for 8weeks at 60° C. (equivalent to about 18 months at 38° C.).

Alkanolamines suitable for the use of the invention include derivativesof ammonia in which one, two, or three hydrogens are replaced by one ormore alkanol groups. Preferably, the alkanolamines are ethanolamines orpropanolamines. Ethanolamines and propanolamines can be obtained byknown processes, e.g., by the reaction of ammonia or a primary orsecondary amine with ethylene oxide or propylene oxide. The reactionproduces a mixture of monoalkanolamine, dialkanolamine, andtrialkanolamine. For instance, the reaction of ammonia with ethyleneoxide produces a mixture of monoethanolamine, diethanolamine, andtriethanolamine. The mixture is often separated by distillation.

Preferably, the alkanolamine is selected from the group consisting ofdiethanolamine, triethanolamine, the like, and mixtures thereof. Morepreferably, the alkanolamine is triethanolamine.

Hydroxylamine or hydrazine is present in the composition in an amounteffective to reduce the discoloration of the alkanolamine. Preferably,hydroxylamine or hydrazine is present in an amount greater than or equalto 10 ppm. More preferably, hydroxylamine or hydrazine is present in thecomposition in an amount greater than or equal to 50 ppm. Mostpreferably, hydroxylamine or hydrazine is present in the composition inan amount greater than or equal to 100 ppm. A particularly preferredrange of hydroxylamine or hydrazine in the composition is from 100 ppmto 1000 ppm.

The preferred triethanolamine is made by a process that comprisesdistilling triethanolamine from the mixture of diethanolamine andtriethanolamine in the presence of phosphorous acid (H₃PO₃). The methodof preparation and distillation of triethanolamine is described in, forexample, U.S. Pat. No. 6,323,371. The patent teachings are hereinincorporated by reference in a jurisdiction where such incorporation isallowed.

Preferably, the composition of the invention further comprises an alkalimetal borohydride. Preferred alkali metal borohydride include sodiumborohydride (NaBH₄) and potassium borohydride (KBH₄). Sodium borohydrideis more preferred.

The alkali metal borohydride is preferably used in an amount greaterthan or equal to 10 ppm. The alkali metal borohydride is more preferablyused in an amount greater than or equal to 50 ppm. The alkali metalborohydride is most preferably used in an amount greater than or equalto 100 ppm.

We have surprisingly found that using an alkali metal borohydride alonedoes not satisfactorily reduce discoloration of the alkanolamine. Whilehydroxylamine or hydrazine alone can effectively reduce thediscoloration of the alkanolamine, a combination of hydroxylamine orhydrazine with an alkali metal borohydride produces significantlyenhanced results in reducing discoloration of the alkanolamine.

The invention includes a method for reducing discoloration ofalkanolamines. The method comprises adding a sufficient amount ofhydroxylamine, hydrazine, or a mixture thereof to an alkanolamine.Suitable alkanolamines and suitable amounts of hydroxylamine andhydrazine are the same as discussed above.

Preferably, the method of the invention further comprises adding analkali metal borohydride to the alkanolamine. Suitable alkali metalborohydrides and their amounts are discussed above.

Preferably, hydroxylamine, hydrazine, alkali metal borohydride are addedto pure alkanolamine. The purity of the alkanolamine is preferablygreater than 95%, more preferably greater than 99%, and most preferablygreater than 99.5%.

The following examples merely illustrate the invention. Those skilled inthe art will recognize many variations that are within the spirit of theinvention and scope of the claims.

EXAMPLES 1-7 AND COMPARATIVE EXAMPLES C8 AND C9

Triethanolamine (TEA) is fractionally distilled from a mixture of TEAand diethanolamine in the presence of 500 ppm phosphorous acid undervacuum. To freshly-distilled TEA samples are added hydroxylamine (50%aqueous solution), hydrazine (35% aqueous solution), or their mixtureswith sodium borohydride, respectively, in Examples 1-7.

In Comparative Example C8, only borohydride, but no hydroxylamine orhydrazine, is added.

In Comparative Example C9, no additive is added.

Color stability of the samples is tested at 60° C. for periods of timespecified in Table 1. From Table 1, it can be seen that the compositionscontaining hydroxylamine or hydrazine have much slower discolorationthan pure TEA of Comparative Example C9.

From Table 1, it can also be seen that although sodium borohydride, whenused in combination with hydroxylamine or hydrazine, can enhance thecolor stability, it is much less effective when used alone.

EXAMPLE 10 AND COMPARATIVE EXAMPLES C11 AND C12

TEA is fractionally distilled from a mixture of TEA and diethanolaminein the presence of 1000 ppm phosphorous acid under vacuum. In Example10, a mixture of hydroxylamine and sodium borohydride is added to afreshly-distilled TEA sample. In Comparative Example C11, only sodiumborohydride is added. In Comparative Example C12, no additive is added.From Table 2, it can be seen that the combination of hydrazine andsodium borohydride effectively stabilizes the color of TEA and thatsodium borohydride alone is much less effective.

EXAMPLE 13 AND COMPARATIVE EXAMPLES C14 AND C15

TEA is fractionally distilled from a mixture of TEA and diethanolaminein the absence of phosphorous acid under vacuum. In Example 13, amixture of hydroxylamine and sodium borohydride is added to afreshly-distilled TEA sample. In Comparative Example C14, only sodiumborohydride is added. In Comparative Example C15, no additive is added.From Table 3, it can be seen that the combination of hydrazine andsodium borohydride effectively stabilizes the color of TEA and thatsodium borohydride alone is much less effective.

Comparing the results in Table 2 with the results in Table 3, it can beseen that distilling TEA in the presence of phosphorous acid cansignificantly reduce the initial color of TEA. However, it is theaddition of hydroxylamine or hydrazine that significantly reduces thediscoloration of TEA. TABLE 1 COLOR STABILITY OF TRIETHANOLAMINEDISTILLED IN THE PRESENCE OF 500 PPM PHOSPHOROUS ACID Additives, ppmAPHA Color, days Ex. Sodium after aged at 60° C. No. HydroxylamineHydrazine Borohydride 0 3 7 14 21 28 42 56 1 200 0 0 18 16 23 30 37 3940 50 2 400 0 0 18 17 24 30 37 42 — — 3 0 300 0 18 21 28 40 49 55 — — 4200 0 400 18 9 13 13 18 20 22 26 5 200 0 200 19 — 20 20 25 26 28 30 6200 0 100 19 — 23 25 26 27 29 30 7 0 300 400 18 11 15 17 22 23 — — C8 00 400 18 21 39 44 61 — — — C9 0 0 0 18 56 102 — — — — —

TABLE 2 COLOR STABILITY OF TRIETHANOLAMINE DISTILLED IN THE PRESENCE OF1000 PPM PHOSPHOROUS ACID Additives, ppm APHA Color, days Ex. Sodiumafter aged at 60° C. No. Hydroxylamine Hydrazine Borohydride 0 3 7 14 2128 42 56 10 200 0 400 21 18 18 18 21 23 26 30 C11 0 0 400 21 46 52 66 7078 — — C12 0 0 0 21 67 120 145 162 193 — —

TABLE 3 COLOR STABILITY OF TRIETHANOLAMINE DISTILLED IN THE ABSENCE OFPHOSPHOROUS ACID Additives, ppm Ex. Sodium APHA Color, days after agedat 60° C. No. Hydroxylamine Hydrazine Borohydride 0 3 7 14 21 28 42 5613 200 0 400 52 47 72 85 98 101 — — C14 0 0 400 52 49 88 166 245 269 — —C15 0 0 0 52 343 426 532 605 659 — —

1-16. (canceled)
 17. A method for stabilizing the color of analkanolamine, said method comprising adding to the alkanolamine astabilizer selected from the group consisting of hydroxylamine,hydrazine, and mixtures thereof in an amount within the range of 100 ppmto 1000 ppm based on the weight of the alkanolamine.
 18. The method ofclaim 17, wherein the alkanolamine is selected from the group consistingof diethanolamine, triethanolamine, and mixtures thereof.
 19. The methodof claim 17, wherein the alkanolamine is triethanolamine.
 20. The methodof claim 17 further comprising adding an alkali metal borohydride to thealkanolamine.
 21. The method of claim 17, wherein the alkanolamine has apurity greater than 95%.
 22. The method of claim 17, wherein thealkanolamine has a purity greater than 99%.
 23. The method of claim 17,wherein the alkanolamine has a purity greater than 99.5%.